The present invention relates generally to methods for planarizing semiconductor substrates, and in particular to planarizing solutions and methods of use for removing titanium nitride from the surface of semiconductor substrates using fixed-abrasive pads, and apparatus produced therefrom.
Chemical-Mechanical Planarizing (CMP) processes are often used for forming a flat surface on a semiconductor substrate in the manufacture of electronic devices. CMP processes generally remove material from a substrate surface to create a highly planar surface. A variety of planarizing machines have been developed to carry out such CMP processes.
Planarizing machines for use in CMP processing generally fall into two categories: web-format and fixed-pad format. In each case, a planarizing pad and a planarizing solution are combined to define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of a substrate. The planarizing pad may be of a fixed-abrasive or non-abrasive type. With a fixed-abrasive pad type, abrasive particles are fixedly bonded to a suspension material. Furthermore, the planarizing solution used with a fixed-abrasive pad type is typically a xe2x80x9ccleanxe2x80x9d solution, i.e., substantially devoid of abrasive particles as such abrasive particles are fixedly distributed across a planarizing surface of the planarizing pad. With a non-abrasive planarizing pad, no abrasive particles are associated with the pad, so the abrasive particles are introduced in the planarizing solution. Such planarizing solutions for use with nonabrasive pad types are often slurries of both abrasive particles as well as chemicals to aid removal of material from a substrate.
To planarize the substrate with the planarizing machine, the surface of the substrate is first contacted against the planarizing pad in the presence of the planarizing solution, i.e., a planarizing surface of the planarizing medium. While in contact, the substrate is then moved relative to the planarizing surface of the planarizing medium, generally through lateral, rotational, revolving or orbital movement of the substrate, the planarizing pad or both. Lateral movement is defined as movement in one direction. Rotational movement is defined as rotation about an axis located at the center point of the object in motion. Revolving movement is defined as rotation about some axis located at other than the center point of the object in motion. Orbital movement is defined as rotational or revolving movement combined with oscillation. Different types of movement may be combined, e.g., rotational movement of the substrate and rotational movement of the planarizing pad or revolving and rotational movement of the substrate against a stationary planarizing pad. As is well understood in the art, such relative movement is in a plane substantially parallel to the surface of substrate. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate.
Fixed abrasive pad types are well known in the art of semiconductor wafer processing. See, e.g., U.S. Pat. No. 5,692,950 issued Dec. 2, 1997 to Rutherford et al.; U.S. Pat. No. 5,624,303 issued Apr. 29, 1997 to Robinson; and U.S. Pat. No. 5,335,453 issued Aug. 9, 1994 to Baldy et al. Despite widespread recognition and acceptance of fixed abrasive pads in the processing of semiconductor wafers, effective planarizing solutions for use in the fixed-abrasive planarization of an advantageous barrier material and conductor, i.e., titanium nitride (TiN), are lacking. As a result, the customary processing for planarizing titanium nitride utilizes abrasive slurries with non-abrasive pad types.
One problem with CMP processing is that the planarized surface of the wafer may not be sufficiently uniform across the whole surface of the wafer. In the competitive semiconductor industry, it is also desirable to maximize the throughput of finished wafers. The uniformity of the planarized surface and maximization of throughput is a function of the effectiveness and repeatability of the planarizing solution utilized with the planarizing pad, as well as a wide array of other CMP operating parameters. While a wide variety of planarizing solutions are available, these solutions are generally specific to the composition of the material to be removed as well as the type of planarizing pad used. For obvious reasons, planarizing solutions developed for non-abrasive pad types are ill suited for use with fixed-abrasive pad types. Therefore, it would be desirable to develop effective planarizing solutions for planarization of titanium nitride on the surface of a semiconductor wafer for use in conjunction with fixed-abrasive planarizing pads.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for methods of planarizing titanium nitride using fixed-abrasive planarizing pads.
In one embodiment, the invention provides a method of planarizing titanium nitride on a surface of a substrate. The method includes contacting the surface of the substrate with a planarizing surface of a planarizing medium, the planarizing medium comprising a fixed-abrasive planarizing pad and a clean planarizing solution. The method further includes moving the surface of the substrate relative to the planarizing surface of the planarizing medium, thereby abrading the titanium nitride on the surface of the substrate. In another embodiment, moving the surface of the substrate relative to the planarizing surface of the planarizing medium comprises moving at least one of the substrate and the planarizing surface of the planarizing medium in a manner selected from the group consisting of lateral, rotational, revolving and orbital. In a further embodiment, the planarizing solution is an etchant solution. In a still further embodiment, the planarizing solution is an oxidizing solution.
In another embodiment, a method of planarizing titanium nitride on a surface of a substrate includes use of an etchant solution as the planarizing solution, wherein the etchant solution contains an etchant and a buffer in aqueous solution. In one embodiment, the etchant comprises at least one etching agent selected from the group consisting of oxalic acid, ascorbic acid and phosphoric acid. In a further embodiment, the buffer comprises at least one buffering agent selected from the group consisting of ammonium acetate, ammonium oxalate, ammonium phosphate and diammonium phosphate. In a still further embodiment, the etchant solution has a pH of approximately 1 to 5. In yet another embodiment, the etchant solution has a pH of approximately 1.5 to 3.
In a further embodiment, a method of planarizing titanium nitride on a surface of a substrate includes use of an oxidizing solution as the planarizing solution, wherein the oxidizing solution contains an oxidizer and a buffer in aqueous solution. In one embodiment, the oxidizer comprises at least one oxidizing agent selected from the group consisting of ammonium persulfate, ammonium heptamolybdate, ceric ammonium nitrate, ceric ammonium sulfate and hydrogen peroxide. In another embodiment, the buffer comprises at least one buffering agent selected from the group consisting of phosphoric acid, ammonium acetate, ammonium oxalate, ammonium phosphate and diammonium phosphate. In yet another embodiment, the oxidizing solution has a pH of approximately 1 to 6. In a further embodiment, the oxidizing solution has a pH of approximately 1.5 to 4.
In one embodiment, the invention provides a method of planarizing titanium nitride on a surface of a substrate. The method includes contacting the surface of the substrate with a planarizing surface of a planarizing medium, the planarizing medium comprising a fixed-abrasive planarizing pad and a clean planarizing solution, wherein the planarizing solution is an aqueous solution comprising approximately 1% to 5% by weight of oxalic acid and approximately 2% to 10% by weight of ammonium acetate. The method further includes moving the surface of the substrate relative to the planarizing surface of the planarizing medium, thereby abrading the titanium nitride on the surface of the substrate.
In another embodiment, the invention provides a clean aqueous planarizing solution. The clean aqueous planarizing solution includes an etchant having at least one etching agent selected from the group consisting of oxalic acid, ascorbic acid and phosphoric acid, and a buffer. In one embodiment, the buffer comprises at least one buffering agent selected from the group consisting of ammonium acetate, ammonium oxalate, ammonium phosphate and diammonium phosphate. In a further embodiment, the planarizing solution has a pH of approximately 1 to 5. In a still further embodiment, the planarizing solution has a pH of approximately 1.5 to 3. In another embodiment, the planarizing solution has approximately 1% to 10% by weight of the etchant and approximately 0% to 10% by weight of the buffer. In yet another embodiment, the planarizing solution has approximately 1% to 5% by weight of the etchant and approximately 0% to 10% by weight of the buffer. In another embodiment, the planarizing solution has approximately 1% to 5% by weight of oxalic acid and approximately 2% to 10% by weight of ammonium acetate.
In a further embodiment, the invention provides a clean aqueous planarizing solution. The clean aqueous planarizing solution includes an oxidizer having at least one oxidizing agent selected from the group consisting of ammonium persulfate, ammonium heptamolybdate, ceric ammonium nitrate, ceric ammonium sulfate and hydrogen peroxide, and a buffer. In one embodiment, the buffer comprises at least one buffering agent selected from the group consisting of phosphoric acid, ammonium acetate, ammonium oxalate, ammonium phosphate and diammonium phosphate. In another embodiment, the planarizing solution has a pH of approximately 1 to 6. In yet another embodiment, the planarizing solution has a pH of approximately 1.5 to 4. In a further embodiment, the planarizing solution has approximately 1% to 10% by weight of the oxidizer and approximately 0% to 10% by weight of the buffer. In a still further embodiment, the planarizing solution has approximately 1% to 5% by weight of the oxidizer and approximately 0.5% to 3% by weight of the buffer.
Further embodiments of the invention provide planarizing solutions and methods of removing titanium nitride of varying scope. Still further embodiments of the invention provide apparatus of varying scope produced in accordance with methods and planarizing solutions of the invention.